1. Field of the Invention
The invention relates to the field of instrumentation control where the operation of the instrument depends upon liquid flow rate. More particularly, the invention relates to flow monitoring in liquid chromatographic apparatus. By way of further characterization but not by way of limitation thereto, the invention is an apparatus for monitoring the flow of the eluent/reagent mixture in a liquid chromatography apparatus and turning off the apparatus if flow rates fall outside predetermined operating parameters.
2. Description of the Related Art
An amino acid analyzer is a specialized application of a liquid column chromatographic separation technique which utilizes ion exchange resin as the stationary phase, with eluting buffers of varying pH and salt concentration employed as the moving phase. Amino acids contained in a sample introduced onto the top of the column are separated from each other as they are eluted through the resin bed which comprises the column packing. For amino acid analysis, the method of choice for detecting the amino acids in the effluent stream has been to combine the column effluent with a reagent which is metered into the stream at a flow rate which is proportional to that of the column eluent. The reagent, upon combining with amino acids present in the stream, forms compounds which, when subjected to a further development process, can be detected by specific changes in optical properties.
An amino acid analyzer may be automated such that samples are automatically injected into the column in a cyclic manner. The physical parameters (flow rates, temperature) of each analysis are repeated with close precision for each sample. It is important that the flow rate of the eluting buffer remain constant during an analysis and that the metering ratio of column effluent and reagent be constant. In addition, especially during periods of unattended automatic operation, it is important that the flow rate of the analyzer be monitored and the analyzer shut down if flow conditions move outside of specified tolerances.
Prior devices require the operator to adjust the flow rates by individually adjusting the pump stroke displacement of each of the pumps, a laborious and time consuming process. In addition, existing flow monitor devices require painstaking adjustment for each flow rate selected. These adjustments require a certain level of intuitive skill not attained by all operators, hence the systems malfunction. That is, the operator adjusts the flow monitor reference point while the analyzer is operating normally such that a warning light would just go on. He would then back off the adjustment until the warning light goes out. The sensitivity thus achieved is such that any small change in flow rate could trigger the warning light. The intuitive skill required comes from knowing how much to adjust the reference point such that the warning light will go on when the flow rate drops to an unsafe level, yet not adjust the reference point so close that a small transient in flow rate will trigger the alarm.